I bet when this pony sheds out, it will be chestnut with flaxen mane/tail. This looks a lot like my first pony that I got for Christmas on my 8th b-day. Decided to test whether there really was a Santa Claus or not and put a note on the Christmas tree on Christmas Eve. Got up the next morning and there was a pony outside with a big red bow!
i had a shetland that was very close to that color and she was consitered a silver dapple or a bay dapple that is on a bay based coat(main and tail are often light) you can see pics of both at http://www.equinecolor.com/silver.html
I don't think she'll lighten up in the summer.. My trainer has an identical colored shetland gelding (hes not registered though) and he gets a little lighter, but his coat doesn't seem to be red-based at all (like a chestnut).. I think silver dapple shetlands are common, at least more so than in other breeds.